Portable volume cycle respirator

ABSTRACT

A portable respirator, of the volume cycle type, is powered by and supplied with compressed medicinal gas, requiring no electric power. The respirator is capable of operating in an automatic mode in which a fixed volume of gas is supplied to the patient for a first selected period of time, exhalation is prevented for a subsequent second period of time, and then the patient is allowed to exhale for a subsequent third selected period of time. The respirator can also operate in a demand mode, in which each cycle is triggered by the attempt of the patient to inhale. The respirator shifts automatically from demand mode to automatic mode cycling and triggers an alarm in the event that the patient becomes too feeble to attempt to inhale. The respirator may also be used as an anesthesia ventilator during surgery.

United States Patent [191 Stewart Oct. 7, 1975 PORTABLE VOLUME CYCLE RESPIRATOR [75] Inventor: Jeffrey Lee Stewart, New York,

[73] Assignee: Bio-Med Devices, Inc., Stamford,

Conn.

[22] Filed: Feb. 25, 1974 [21] Appl. No.: 445,758

abandoned.

[52] US. Cl. 128/l45.8; 128/203; 128/188 [51] Int. Cl A61m 16/00 [58] Field of Search 128/145.8, 145.6, 145.5,

l28/146.4, 146.5, 142.2, 142.3, 142.4, 188, 191, 197, 202, 203, 2.08, 297, 142.7, 142, DIG. 17; 73/401,137/62414; 235/201 ME [56] References Cited UNITED STATES PATENTS 3,191,596 6/1965 Bird 128/145.5 3,221,734 l2/1965 Beasley.. 128/145.8

3,265,061 8/1966 Gage l28/145.8 3,316,902 5/1967 Winchel 128/DIG. 17 3,357,428 12/1967 Carlson 128/DIG. 17

3,434,471 3/1969 Liston l28/145.8 3,508,542 4/1970 Browner.... l28/l42.2

3,561,466 2/1971 Carden 128/188 3,604,415 9/1971 Hoenig 128/145.8

7074; was ezack 0/4644 0U/VMNT, net $5025 2 F'l/EF new can/near. 3 V4045 waves 54- 6 o ,P/s/a 74M Maw/wires .3!

3,669,108 6/1972 Sundblom 128/1422 R26,5ll 12/1968 Hewson l28/145.8

FOREIGN PATENTS OR APPLlCATlONS 705,723 10/1936 Germany 128/202 393,650 9/1924 Germany 128/142.3

Primary Examiner-Richard A. Gaudet Assistant Examiner1-1enry J. Recla Attorney, Agent, or FirmBlum, Moscovitz, Friedman & Kaplan [5 7 ABSTRACT A portable respirator, of the volume cycle type, is powered by and supplied with compressed medicinal gas, requiring no electric power. The respirator is capable of operating in an automatic mode in which a fixed volume of gas is supplied to the patient for a first selected period of time, exhalation is prevented for a subsequent second period of time, and then the patient is allowed to exhale for a subsequent third selected period of time. The respirator can also operate in a demand mode, in which each cycle is triggered by the attempt of the patient to inhale. The respirator shifts automatically from demand mode to automatic mode cycling and triggers an alarm in the event that the patient becomes too feeble to attempt to inhale. The respirator may also be used as an anesthesia ventilator during surgery.

13 Claims, 18 Drawing Figures f y/4 7- .Exx/nosr rare (5) 70 50/20 7 24 p/saw J .S'UPPl/ES O :PIASSUAE (EEK/(4701? PIESSUIE 5405s {yr/47512 U.S. Patent Oct. 7,1975 Sheet 1 of 16 3,910,270

w Q m US. Patent Oct. 7,1975 Sheet 5 of 16 3,910,270

US. Patent Oct. 7,1975 Sheet 6 of 16 3,910,270

LOG/C 0646/84/14 DEA/4W0 M005 Sheet 7 of 16 3,910,270

U.S. Patent Oct. 7,1975

unvu V U.S. Patent Oct. 7,1975 Sheet 12 of 16 3,910,270

U.S. Patent Oct. 7,1975 Sheet 13 of 16 3,910,270

US. Patent Oct. 7,1975 Sheet 15 0f 16 3,910,270

U.S. Patent Oct. 7,1975 shw 16 of 16 3,910,270

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W ME k m Rug PORTABLE VOLUME CYCLE RESPIRATOR This is a continuation, of application Ser.. No. 287,936, filed Sept. 11', 1972, now abandoned.

BACKGROUND OF THE iNvENnoN The use of a respirator is indicated in a wide variety of medical conditions such as chronic pulmonary emphysema, chronic bronchitis, pulmonary edema, dyspnea, pneumoconiosis, pulmonary arteriosclerosis, bronchial asthma, among others. It is also applicable for use during surgery as an anesthesia ventilator, for postoperative support, in treatment of a patient who is comatose or in shock, and, in short, in support of any patient unable to maintain normal autonomous respiration.

In the design of a respirator, it must be taken into 'account that the respirator may be used in a hospital or in surroundings where no electrical power is available, and, moreover, the respirator must be suitable for use with patients of any age from infancy through adulthood to geriatric.

Respirators fall into two categories, either( 1) pressure cycled or (2) volume cycled. In the first category,

medicinal gas, which includes filtered air, oxygen and mixtures containing oxygen is supplied to the patient until a fixed pressure is reached. In the second type, medicinal gas is supplied to the patient until a fixed volume has been transferred. Pressure cycled respirators, up to now, have been more popular because of the fact that the mechanism involved is relatively simple and the cost, consequently, is relatively low. The principle control device in such a respirator is some type of pressure-actuated valve having various combinations of di aphragms, springs, magnets, etc. which switch from supply to exhaust when a pre-set pressure is reached. They have the additional advantages of being small, light-weight and consequently easily portable. In general, they have means for allowing triggering of the supply of gas by means of an attempt by the patient to inhale. The principle disadvantage of this type of respirator is that it cannot maintaindelivery of a pre-set volume of gas to the patient if resistance to gas flow develops either in the air-way to the patient or in the patient himself.

The volume-cycled respirator has the important advantage of being able to deliver a constant tidal volume independent of a change in the patients compliance and resistance developing in the air-way. Moreover, it is possible to include accessory features with a volume cycled respirator. Such features are periodic maximal inflation (sigh), effective humidification of the medical gas, multiple alarm systems informing the operator of various types of difficulties which may occur and simple adjustment of the quantity of medical gas to be supplied to the patient.

Volume-cycled respirators of the prior art have been high in cost, and of large size and weight, as the result of which they have not been truly portable. Moreover, they have involved a large number of components and moving parts, resulting in the need for frequent maintenance and presenting problems of reliability. Also, in common with pressure cycled respirators it has not been possible to vary the amount of gas delivered over a sufficiently wide range so that a single unit could be used in the treatment of both pediatric andadult patients. Finally, no unit is available which can be powered by pressurized gas alone.

SUMMARY OF THE INVENTION Pressurized medicinal gas is supplied at a constant flow rate to a rigid tank. An air supply tube runs from the rigid tank to a means for connecting the tube to a patient. The means may be a face mask, a nose mask or even a tube inserted into the trachea of the patient. Intermediate of the rigid tank and the patient are a normally closed valve, a fine filter and a humidifier.

A signal generator using pneumatic logic, powered either by the source of medicinal gas or by an auxiliary source of compressed air which need not be as pure as the medicinal gas, opens a normally closed valve in the main air-way to the patient for a fixed period. Close to the end of the main air-way connecting with the patient is a side tube at the end of which is a normally open valve. The normally open valve on the side tube is held in closed position by a signal from the signal generator when medicinal gas is being supplied to the patient. At the end of the fixed period which is adjustable, the valve and the main air-way are closed, and shortly thereafter the signal to the valve in the side tube is cut off. At this point the side-tube valve opens and the patient exhales through the side tube. It should be noted that the system is fail-safe in that disconnection of the signal generatorfrom its source of pressurized gas allows the exhaust valve to open so that the patient can breath through the side tube.

As aforenoted, medicinal gas is supplied to the rigid tank at a fixed rate. During inhalation, the pressure in the rigid tank drops and during exhalation the pressure in the rigid tank rises to its original value. In the event that the compliance of the patient increases or resistance in the main air tube increases, the volume of air delivered to the patient will decrease on the first cycle after the resistance develops. As a consequence, the pressure in the rigid tank will not drop as far as it normally would during inspiration, and on the next expiration the pressure will rise to a value higher than normal. Since the rigid tank is being supplied with gas at a constant rate, the pressure in the tank will rise until the volume delivered to the patient on each cycle will equal the volume delivered to the tank during each cycle, thus restoring the conditions under which the patient is fed with the desired quantity of medicinal gas on each cycle.

In the event that the patient is too weak to make any attempt to inhale, the signal generator logic operating the medicinal gas supply under the conditions described is said to be operating in automatic mode. However, it is possible to modify the logic so that each cycle of inspiration and exhalation is initiated or triggered by an attempt of the patient to inhale. Under such conditions, the respirator is said to be operating in the demand mode. This method of operation is preferable when the patient is strong enough to attempt to breath. However, it carries-with it the dangers that the patient may become enfeebled and too weak to attempt to inhale. The present invention includes a shift circuit which changes the mode of operation from demand to automatic in the event that the patient fails to attempt to inhale within a pre-set number of seconds subsequent to the end of exhalation.

The logic includes a maximal inflation circuit termed .a sigh circuit which provides for a deeper inhalation after a preset number of inhalations of normal volume.

Where a respirator is being used in a region such as a hospital where a supply of compressed air is usually available, the compressed air, if properly filtered, can be used both for the main source of medicinal gas and as the power for the logic circuit. An automatic substitution circuit is provided in the present invention so that if the main supply of compressed air fails, connection is automatically made to an auxiliary tank which may contain either compressed air or medicinal gas. In this way, the patient is protected against failure of the main supply.

An object of the present invention is to provide an improved volume cycled respirator which is powered by pressurized gas alone and which is portable.

Another object of the present invention is to provide an improved volume cycled respirator utilizing a rigid tank instead of the usual bellows or bag.

A further object of the present invention is to provide an improved volume cycled respirator in which a rigid tank is supplied with a medical gas at a fixed controlled rate.

Still another object of the present invention to provide an improved volume cycled respirator including control by a signal generator consisting of fluidic logic elements and which may be powered either with medical gas or with clean compressed air.

Another object of the present invention is to provide an improved volume cycled respirator which is simple in construction, inexpensive, highly reliable, easy to operate and requiring virtually no maintenance.

Yet another object of the present invention is to provide an improved volume cycled respirator which is sufficiently portable and simple to operate so that it can be used while a patient is in transit in a vehicle such as an ambulance, a police car or a fire engine.

Yet a further object of the present invention is to provide an improved volume cycled respirator suitable for treatment of pediatric, adult and geriatric patients.

Still a further object of the present invention is to provide an improved volume cycled respirator which automatically switches over to an emergency source of medical gas in the event that the main power supply fails.

Yet a further object of the present invention is to provide an improved volume cycled respirator in which provision is made for connecting the patient directly to the ambient atmosphere in the event of complete system failure.

A particularly significant object of the present invention is to provide an improved volume cycled respirator having both visible and audible alarms to indicate any anticipated type of malfunction, including failure of a gas supply and loss by the patient of the ability to attempt to inhale.

A still further object of the present invention is to provide an improved volume cycled respirator which may be used as an anesthesia ventilator.

A further object of the present invention is to provide an improved volume cycled respirator with means for an automatically volume compensated periodic maximal inflation (sigh) wherein the periodic sigh does not change the average rate of supply of medical gas to the patient.

A still further object of the present invention is to provide an improved volume cycled respirator having a cycle in which is present a plateau period at the end of inspiration to allow equilibration of the various compartments of the patients lungs and during which patients alveolar pressure may be measured.

A further object of the present invention is to provide an improved volume cycled respirator having means for accurately mixing a plurality of gases to form a desired medical gas composition.

Yet a further object of the present invention is to provide an improved volume cycled respirator having means for controlling both the inspiratory time and the expiratory time.

Yet another object of the present invention is to provide an improved volume cycled respirator having means for adjusting the expiratory resistance thus providing means for retarding the rate of expiratory flow.

Still another object of the present invention is to provide an improved volume cycled respirator having means for adjusting the end expiratory pressure so that it is either above or below ambient pressure.

Another object of the present invention is to provide means for interconnecting fluidic logic elements without the use of tubing.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.-

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a block diagram showing the principle components of a volume cycled respirator in accordance with the present invention;

FIG. 2 is a block diagram of a volume cycled respirator in accordance with the present invention indicating how gases are mixed to form a suitable feed to a patient, and giving a diagrammatic key to components;

FIG. 3 contrasts essential components of the present invention with analogous components of the prior art;

FIG. 4 is a diagram of the signals emitted by a pneumatic logic system in accordance with the present invention where the respirator is to operate in automatic mode;

FIG. 5 is a schematic diagram of the basic oscillator circuit of the logic system for operating the respirator in automatic mode;

FIG. 6 is a diagram of the signals necessary for operating the respirator in demand mode;

FIG. 7 is a diagram of a signal generator system showing how a demand circuit is coupled with the basic oscillator circuit;

FIG. 8 is a shift circuit which renders the demand circuit inoperative in the event that the patient becomes too feeble to inhale;

FIG. 9 is a diaphragm-operated demand valve in section with a diagrammatic representation of a signal generator for supplying a triggering pulse;

FIG. 10 is a sigh circuit which can be connected to the basic oscillator circuit to cause a deeper inhalation than usual at controlled intervals;

FIG. I] shows how failure of the system or enfeeblement of the patient causes alarms to sound and become visible;

FIG. 12 is a block diagram of the portion of the respirator adjacent to the patient using same;

FIG. 13 shows diagrammatically the valve through which exhalation nonnally takes place and a redundant valve for connection of the patient to the ambient air in case of total system failure;

FIG. I4 is a diagrammatic representation of a circuit which makes it possible to measure the alveolar pressure in the patients lungs at the end of inhalation and alternatively to measure continuous system pressure.

FIG. 15 is a device for maintaining the pressure in the patients lungs above atmospheric at the end of exhalation;

FIG. 16 is a device for lowering the pressure in the patients lungs below atmospheric at the end of exhalation;

FIG. 17 shows schematically how interconnections may be made between fluidic circuit components by means of grooves molded or otherwise formed in flat plates; and

FIG. 18 is a schematic diagram of a simplified signal generator for operating the respirator in automatic mode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of operation of the present invention is exemplified in FIG. 1 where a medical gas supply 21 which may consist of relatively clean compressed air, or oxygen, or an anesthetic is connected to a patient through a quick disconnect 22, a check valve 23, a filter 24, where the filter is fine enough to remove relatively coarse particles and droplets of oil, a pressure regulator 27, an on-off valve 26, a flow meter 28, an adjustable flow control valve 29, a rigid tank 31 having pressure relief valves 32 and 33, a remote-operated normally-closed valve 34, a patient manifold 36 fitted with a fixed maximum pressure relief valve 37 and an adjustable pressure relief valve .38, an ultra-fine filter 39 for preventing infection of the patient, a humidifier 41 which may also be used for medication of the patient and a tube 42 leading to the patient and fitted with connecting means (not shown) which may consist of a face or a nose mask or a tube inserted into the trachea of the patient. Adjacent to the patient is a side tube 43 leading to a normally-open valve 44 through which the patient can exhale. The signals which open normallyclosed valve 34 and close normally-open valve 44 are delivered by signal generator 46. Signal generator 46 consists entirely of fluidic-logic elements powered by pressurized gas supply 47. It is possible to use medical gas supply 21 for powering signal generator 46 but in general it is wasteful of relatively expensive medical gas. The signal from the signal generator which operates normally-closed valves is termed A for convenience and the signal which operates normally-open valve 44 is termed signal B for convenience.

Further detail, particularly with respect to the medical gas supply, is shown in FIG. 2, where, in the example shown, each source has its own quick disconnect 22, check valve 23, filter 24, and regulator 27. The usual medical gas supply, is supplemented with an emergency supply, usually of oxygen. Emergency supply 48 has its own quick disconnect 22, check valve 23, filter 24, and regulator 27. In the event of failure of the regular supply, the pressure in supply line 49 becomes inadequate to hold normally-open valve 51 in closed position whereupon valve 51 opens and the emergency supply 48 of oxygen becomes available to the system. Check valve 52 prevents backward flow of oxygen in the event of failure of the normal medical gas supply. It is convenient to use a single switch for 4 on-off valves 53 which are used in starting up and shutting down the system, three of these being in the medical gas supply lines and the fourth shutting off an audible alarm signal. Flow control valves 54 control the rate of flow of each of the components of the medical gas, the rate of flow being'shownby flow meters 56. The medical gas components flowing through the flow control valves 54 are mixed in rigid tank 31 and then passed through the airway as aforenoted. Line connects the patient manifold to a snap sensor (FIG. 11) in the fluidic logic circuitry 46 the function of which will be detailed below. Valve 57 is normally open and is held closed whenever power is supplied to the signal generator 46. In the event of failure of power to the signal generator, valve 57 opens and furnishes an additional connection between the patient and the ambient atmosphere.

Three-way valve 58 connects pressure gauge 59 either to the patient directly through the main air-way so that continuous system pressure may be measured or to the air-way through signal sampling circuit so that the patients alveolar pressure can be measured.

As aforenoted, the principal differences between the respirator of the present invention and those of the prior art lie in the fact that a rigid tank is used instead of the previous bellows or piston or bag and in the fact that the present system is operated completely by means of pressurized gas so that the assembly is much simpler than those of the prior art. The differences are indicated schematically in FIG. 3.

The wave shapes sent to normally-closed valve 34 and normally-open valve 44 by signal generator 46 are shown in FIG. 4 wherein zero on the ordinate axis indicates the absence of a signal and a one indicates the presence of a signal. The C-pulse is put out by the signal generator in addition to A- and B-pulses, the purpose of the C-pulse being to make it possible to measure alveolar pressure in the lungs of the patient at the end of inhalation. The alveolar pressure is measured in the interval between the end of inhalation which is indicated by time 1 on the abscissa of the diagram and the beginning of exhalation at time 2. The period of time between 1 and 2 is indicated by the letter (1. An interval between the end of exhalation and the beginning of inhalation is also introduced between times 3 and 4 to allow sufficient time to elapse for exhaust valve 44 to close before inlet valve 34 opens. The time interval between numerals 3 and 4 is indicated by the Greek letter delta in FIG. 4. It should be noted that inhalation takes place on the output of the signal whereas exhalation takes place in the absence of a signal from the signal generator due to the fact that valve 34 is normally closed and valve 44 is normally open. The basic oscillator circuit in the signal generator is shown in FIG. 5. The circuit in this form, that is, without accessory circuits, operates in what is termed automatic mode. In this mode, it is assumed that the patient is too feeble to attempt to breath by himself so that medical gas is supplied in selected volume and at a selected frequency to the patient and the elasticity of the patients chest and thorax are relied upon for exhalation over a period which again is adjustable subject to the discretion of an attendant. The pneumatic circuit of FIG. 5 consists of 

1. A portable volume cycle respirator powered by gas pressure alone, comprising means for supplying medical gas to a patient for inspiration during a first period of time, pneumatic logic means for preventing, for a preselected second period of time exhalation of gas by said patient subsequent to said first period, valve means for permitting exhalation of gas by said patient during a third period of time subsequent to said second period of time.
 2. A portable volume cycle respirator powered by gas pressure alone as defined in claim 1 wherein the pneumatic logic means includes a pneumatic oscillator circuit comprising first and second sources of pressurized gas; first normally-closed fluidic gate means having an output port, a dump port, an input port connected to said first source of pressurized gas, adjustable first flow restrictor means connected between said first source of pressurized gas and said input port, and a control port, said first gate means output port being normally connected to said dump port for flow of gas internally from said output port to said dump port, and being connected internally to said input port to receive pressurized gas therefrom when pressurized gas is applied to said control port; second flow restrictor means connected to said first gate means dump port to control the rate of flow of gas therethrough; second fluidic gate means having first and second control ports, a dump port, an input port connected to said second source of pressurized gas, an output port connected to said first control port to apply pressurized gas thereto, and valve means responsive to gas pressure applied to said first and second control ports and said input port, said second gate means output port being connected internally to the associated input port when the sum of the pressures at said input port and said first control port exceeds the pressure at said second gate port by a predetermined amount and being connected to the associated dump port when the pressure at said second control port exceeds the sum of the pressures at said first control port and said input port by a predetermined amount; fluidic output circuit means connected to said second gate means output port for transmitting the oscillatory output signal produced at said second gate means output port; feedback means connecting said output circuit means and said first gate means control port; fluidic circuit means connecting said first gate means output port and said second gate means second control port and including first reservoir means for controlled filling and emptying in response to the state of said first gate means to apply pressurized gas to said second gate means second control port.
 3. A portable volume cycle respirator powered by gas pressure alone as defined in claim 2, wherein the pneumatic logic means includes a pneumatic circuit further comprising a sigh circuit which at predetermined periods places a fourth flow restrictor in series with said second flow restrictor, thereby periodically increasing the duration of the pulse put out by said oscillator circuit.
 4. A portable volume cycle respirator powered by gas pressure alone as defined in claim 2, wherein the pneumatic logic means includes a pneumatic circuit said fluidic output circuit means includes first time delay means for shaping said oscillatory output signal.
 5. A portable volume cycle respirator powered by gas pressure alone, as defined in claim 4, wherein the pneumatic logid means includes a pneumatic circuit said first time delay means includes third fluidic gate means having a control port, an input port and a dump port, said third fluidic gate means input port being internally connected to the associated dump port when pressurized gas is not applied to the associated control port; second reservoir means having an input and an output; third flow restrictor means connected to said second reservoir means input; and fluidic circuit means connecting the series connection of said second flow restrictor means and said second reservoir means between said third gate means control port and input port.
 6. A portable volume cycle respirator powered by gas pressure alone as defined in claim 5, wherein the pneumatic logic means includes a pneumatic circuit said output circuit means further comprises a fourth fluidic gate means having a control port, an input port, an output port and a dump port; a third source of pressurized gas connected to said input port, fluidic circuit means connecting said input port of said fourth fluidic gate means with said output port of said second fluidic gate means and said output port of said fourth fluidic gate means with said input port of said third gate means, said fourth gate means output port being alternately connected internally to one of said associated input and dump ports in response to the presence or absence of pressurized gas at the associated control port; fifth gate means having valve means, biasing means acting in said valve means, first and second control ports, an input port, an output port and a dump port; fourth and fifth sources of pressurized gas connected respectively to said first control port and said input port of said fifth gate means; and fluidic circuit means connecting the input port of said third gate means with said second control port of said fifth gate means, said input and said output ports of said fifth gate means being internally connected by said valve means when the pressure at said second control port of said fifth gate means plus the force exerted by said biasing means exceeds the pressure of said fourth source of pressurized gas by a predetermined amount, and said output port and said dump port of said fifth fluidic gate means being internally connected when the pressure of said fourth source of pressurized gas exceeds the sum of the forces of pressurized gas at said associated second control port and said biasing means.
 7. A portable volume cycle respirator powered by gas pressure alone as defined in claim 6, wherein the pneumatic logic means includes a pneumatic circuit comprising fluidic circuit means connecting said output port of said fifth gate to said control port of said first gate.
 8. A portable volume cycle respirator powered by gas pressure alone as defined in claim 1 wherein the pneumatic logic means includes pneumatic oscillator circuit comprising a first fluidic gate means having a control port, a supply port, a dump port and an output port, a first pressurized gas supply connected to said input port, an adjustable first flow restrictor in said connection between said first source of pressurized gas and said supply port, a second flow restrictor connected to said dump port and a reservoir connected to said output port, said outpuT port being normally connected internally to said dump port, a second fluidic gate means having a control port, a supply port, an output port, and a dump port, a second pressurized gas supply connected to said input port, first reservoir means in said line connecting said first gate output port with said second gate control port, fluidic output means connected to said second gate means output port for transmitting the oscillatory output signal produced at said second gate means output port; feedback means connecting said output means connecting said output circuit means and said first gate means control port; said first reservoir means serving for controlled filling and emptying in response to the state of said first gate means to apply pressurized gas to said second means second neutral port.
 9. A portable volume cycle respirator powered by gas pressure alone as defined in claim 8, wherein the pneumatic logic means includes a pneumatic circuit further comprising a third fluidic gate means having a control port, an input port and a dump port, said control port being connected to the output port of said second fluidic gate means, a third flow restrictor and a second reservoir connected in series in that order between said control and input ports of said third gate means, said third gate means with said third flow restrictor and said second reservoir constituting a delay means.
 10. A portable volume cycle respirator powered by gas pressure alone as defined in claim 9, wherein the pneumatic logic means includes a pneumatic circuit further comprising a fourth pneumatic gate means having a first control port, an input port, a dump port and an output port, a third pressurized gas supply means connected to said input port, a third reservoir connected to said output port means and a fourth flow restrictor connected to said dump means, said control port of said fourth fluidic gate means being connected to said output port of said second fluidic gate means.
 11. A portable volume cycle respirator powered by gas pressure alone as defined in claim 10, wherein the pneumatic logic means includes a pneumatic circuit further comprising a fifth pneumatic gate means having a control port, an input port, an output port, and a dump port, said control port being connected to said control port of said first fluidic gate means, said third reservoir having an output line connected to said input port of said fifth gate.
 12. A portable volume cycle respirator powered by gas pressure alone as defined in claim 8, wherein the pneumatic logic means includes a pneumatic circuit further comprising a sigh circuit which at predetermined periods places a fourth flow restrictor in series with said second flow restrictor, thereby increasing the duration of one of the signals put out by said oscillator circuit.
 13. A portable volume cycle respirator powered by gas pressure alone as defined in claim 1, including means for indicating pressure failure within said respirator and indicating termination of breathing by a user, said means including an audible oscillator circuit and an audible signal actuator, said audible oscillator circuit comprising a pneumatic gate having a control port, first, second and third output port, a gate diaphragm biased to hold said first output port closed, a first orifice connected to said first output port, a tank and a second orifice connected in sequence between said conrol port and said second output port, said third output port being automatically connectable to a source of non-pulsating pressurized gas in case of an emergency when it is desirable to sound an alarm, said gate diaphragm closing said third output port when said input port is pressurized, said audible signal actuator comprising a diaphragm valve having an input port connected to said second output port of said gate, said valve diaphragm being biased toward said input port, a rod so connected at one end thereof to said valve diaphram as to move to and fro in an axial direction in consonance with movement of said valve diaphragm, and a bell the other end of said rod protruding outward from said diaphragm and being positioned to strike said bell when moved by said valve diaphragm. 